1. Field of the Invention
The present invention relates to control operation between communication apparatuses for communication between a wireless LAN (Local Area Network) access-point apparatus and a communication terminal apparatus. More particularly, the present invention relates to a wireless communication system and a wireless communication apparatus having a dynamic frequency selection (DFS) function, a wireless LAN system, a wireless LAN access-point apparatus, a wireless LAN terminal apparatus, a wireless communication method, and a computer readable recording medium recording a wireless communication program.
2. Description of the Related Art
A frequency band of 5 [GHz] (5.25 to 5.35 [GHz]) is used for a wireless LAN, as a wireless communication system, in conformity with IEEE (Institute of Electrical and Electronics Engineers) 802.11a. The frequency band is assigned to a weather radar, and electrical waves of the weather radar are received by a wireless LAN access point. The electrical waves of the weather radar are out-of-target electronic waves for the wireless LAN access point. At the wireless LAN access point, the electrical waves of the weather radar are detected, and the DFS function operates, thereby changing channels during the communication. With the DFS function, the channel is changed upon detecting the electrical waves of the weather radar and the interference against the electrical waves of the weather radar is prevented. In Japan, similarly to United States or Europe, using frequencies of the wireless LAN are assigned to the frequency band identical to that of the electrical waves of the weather radar. Therefore, the frequency change and channel change are required.
With respect to this DFS function, PCT Japanese Translation Patent Publication No. 2004-535095 discloses that a plurality of frequencies are monitored and estimated continuously or quasi-continuously and a quality parameter indicating the probability for sharing the frequency is assigned to each frequency in order to control the frequency selection (refer to summary, etc.).
Meanwhile, the DFS function operates and communication between connections, i.e., communication between a wireless LAN terminal apparatus and a wireless LAN access point is interrupted. Needless to say, a term for interrupting the communication damages reception and transmission of information. As a consequence, the reduction of the communication interruption term is required.
This problem is not disclosed in PCT Japanese Translation Patent Publication No. 2004-535095 and solution means thereof neither is suggested nor disclosed.